In a fuel supply apparatus for supplying a fuel to an internal combustion engine, a high-pressure fuel supplied from a high-pressure pump is accumulated in a fuel accumulator. The accumulated high-pressure fuel is injected into a combustion chamber of the engine through a fuel injector. A high-pressure pump is equipped with a relief valve. When the fuel pressure in the fuel accumulator is excessively raised beyond an allowable value due to a malfunction in a suction valve or a discharge valve of the high-pressure valve, the relief valve is opened to relieve the high-pressure fuel into a return passage.
In a high-pressure pump shown in JP-2004-138062A, a discharge passage and a relief passage are arranged in parallel with each other. The discharge passage is formed for pressure-feeding the fuel in a pressurization chamber to a discharge port through a discharge valve. The relief passage is formed for returning the fuel of excessive pressure in a fuel accumulator from the discharge port to the pressurization chamber through a relief valve. When the high-pressure pump discharges the fuel, the fuel pressure in the pressurization chamber acts to open the discharge valve, and simultaneously acts in such a direction that the relief valve is abutted against a seat portion. Therefore, even when the fuel pressure in the pressurization chamber exceeds a relief valve opening pressure at the time of discharge, the relief valve is not opened. As a result, a part of discharged fuel is prevented from flowing out of the relief valve and the accuracy of metering is ensured.
In the high-pressure pump shown in JP-2004-138062A, a chamber for accommodating the discharge valve and a chamber for accommodating the relief valve are separately independently formed in a housing, whereby a lot of high-pressure seals are necessary therebetween.
In the high-pressure pump shown in U.S. Pat. No. 7,401,593 B2, a chamber for accommodating a discharge valve and a chamber for accommodating a relief valve are separately formed in a bottom of one large hole (chamber). Then, a discharge connector is joined to the opening of the large hole. The number of points where a high-pressure seal is necessary is thereby reduced.
In the high-pressure pump shown in JP-2010-174903A, a fuel is returned to a low-pressure area, not to a pressurization chamber, when a relief valve is opened. When the fuel is discharged, the relief passage from the discharge port to the relief valve is closed in conjunction with a lifting of a discharge valve. As a result, when the fuel pressure in a pressurization chamber exceeds a relief valve opening pressure, it can be avoided that the relief valve is opened and a part of discharged fuel flows out, so that an accuracy of metering is ensured.
In the high-pressure pump disclosed in JP-2004-138062A, a cylindrical member forming the valve seat of the discharge valve is press-inserted into an inner wall of the housing of the high-pressure pump. For this reason, a force from the inner wall of the housing is exerted on the cylindrical member forming the valve seat of the discharge valve in an inward radial direction.
In the high-pressure pump disclosed in U.S. Pat. No. 7,401,593 B2, a closed-end cylindrical holder is welded or calked on the outer wall of a member forming the valve seat of the discharge valve. The holder holds a biasing member for biasing a discharge valve member in a valve-close direction. For this reason, a force from the holder is exerted on the member forming the valve seat of the discharge valve in the inward radial direction due to welding or calking.
In the high-pressure pumps disclosed in JP-2004-138062A and U.S. Pat. No. 7,401,593 B2, a discharge passage and a relief passage are arranged in parallel with each other and both of them communicate with a pressurization chamber. For this reason, in addition to the fuel in the pressurization chamber, the fuel in the discharge passage and the relief passage is simultaneously pressurized during a pressurization stroke. That is, in the high-pressure pumps in JP-2004-138062A and U.S. Pat. No. 7,401,593 B2, “dead volume” other than the pressurization chamber is increased, which deteriorates a discharging efficiency of a high-pressure pump.
In the high-pressure pump shown in JP-2010-174903A, the dead volume is not increased. However, the configuration of a discharge valve is complicated and high machining accuracy is required, which increases its manufacturing cost. A fuel pressure pulsation in the high-pressure pipe from the high-pressure pump to the fuel accumulator has great influence on the lift of the discharge valve. The fuel pressure pulsation is varied depending on a bend position, a bend angle, and the like in high-pressure pipe as well as the engine speed and the discharge rate of a pump. It is necessary to tune various elements of a discharge valve for individual engines. This increases a manufacturing cost.
In the high-pressure pumps shown in JP-2004-138062A, U.S. Pat. No. 7,401,593 B2, and JP-2010-174903A, a discharge valve and a relief valve are provided in different passages and it is necessary to form chambers accommodating the both valves. This increases a physical size of the housing and its manufacturing cost.
When a force from the inner wall of the housing is exerted on a member forming the valve seat of a discharge valve in the inward radial direction, there is a possibility that the valve seat portion is deformed. When the valve seat portion is deformed, the tight abutment between the valve seat and a discharge valve member is prevented and there is a possibility that discharge pressure is reduced or destabilized.
In the high-pressure pump shown in JP-2004-138062A, a member forming the valve seat of the discharge valve is just press-inserted into the inner wall of the housing. Therefore, it is likely that the member may get out of the inner wall of the housing due to an internal pressure established when the high-pressure pump is in operation.
Also, the high-pressure pump in JP-2004-138062A is provided with the relief valve for returning the fuel to the pressurization chamber of the high-pressure pump when the fuel pressure becomes greater than a predetermined value. A cylindrical member forming the valve seat of this relief valve is press-inserted into the inner wall of the housing of the high-pressure pump. Therefore, the same problem as mentioned above may occur with respect to the member forming the valve seat of the relief valve.
When a force from a holder is exerted on the member forming the valve seat of the discharge valve in the inward radial direction, there is a possibility that the valve seat portion is deformed. When the valve seat portion is deformed, the tight abutment between the valve seat and a discharge valve member is prevented and there is a possibility that discharge pressure is reduced or destabilized.
Also, the high-pressure pump in U.S. Pat. No. 7,401,593 B2 is provided with the relief valve for returning fuel to the pressurization chamber of the high-pressure pump when the pressure of fuel becomes greater than a predetermined pressure. A closed-end cylindrical holder that holds a biasing member for biasing a relief valve member in a valve-close direction is welded or calked on the outer wall of a member forming the valve seat of this relief valve. Therefore, the same problem as mentioned above may occur with respect to the member forming the valve seat of the relief valve.